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  1. johannestoger

    Air cylinder friction

    @ornerynorsk: It will be a fresh charge of water in every pulse, i.e. we'll fill the pump from a fresh water source on the inward stroke, and empty the pump into the experiment on the outward stroke. @FACS: Thanks, great to hear some input from an expert. I should mention also that we need the...
  2. johannestoger

    Proportional valve for water, low pressure

    @btrueblood: Thanks, I'll keep the cylinder roughness in mind.
  3. johannestoger

    Piston/cylinder pulsatile pump - seal using O-rings?

    @hydtools: Ah, PTFE is a great idea. Thanks!
  4. johannestoger

    Proportional valve for water, low pressure

    @btrueblood: Would plastic tubing, e.g. PVC work? Or is polished metal a better choice to minimize wear on the O-ring? I submitted the cylinder/piston idea to the fluid mechanics forum, feel free to chip in there: http://www.eng-tips.com/viewthread.cfm?qid=342215
  5. johannestoger

    Piston/cylinder pulsatile pump - seal using O-rings?

    Hi, I'm a medical imaging engineer well outside my comfort zone - I hope you can give some insight on a flow experiment I'm designing. We're trying to generate a controlled pulsatile flow in a 1" pipe. The peak flow is around 0.6 m/s (2 ft/s), and the pulse should go from zero to peak to zero...
  6. johannestoger

    Proportional valve for water, low pressure

    Thanks everyone for great answers!
  7. johannestoger

    Air cylinder friction

    Hi fellow engineers, I'm a medical imaging engineer way outside my comfort zone, and I hope you can give some insight. We're trying to generate fast, accurate pulses of water in a 1" pipe. We want a peak velocity of 0.6 m/s and a pulse lenght of 300 ms. Our current idea is to take a 1"...
  8. johannestoger

    Proportional valve for water, low pressure

    @gerhardl - Thanks, I'll look into it. By controlled pulse I mean that I'd like the flow to vary as v = V*sin2(pi*t/T). Here T is the pulse time, about 300 ms and V is the peak flow, about 0.6 m/s.
  9. johannestoger

    Proportional valve for water, low pressure

    Thanks a lot for very good answers! @btrueblood: The plunger idea sounds interesting. We have been discussing putting a piston in a pipe, as in the diagram below, is this what you are thinking of? This design has some nice advantages, including that we can get very exact and repeatable...
  10. johannestoger

    Proportional valve for water, low pressure

    Oh and another thing - the Burkert and Danfoss valves have a stated minimum pressure of 7 psi (0.5 bar). The highest we can go in the current design is about 1.5-1.7 psi. So I'm thinking: Will these valve not open at all at lower pressures? Or will they work, but not optimally?
  11. johannestoger

    Proportional valve for water, low pressure

    OK, thanks, I'll look into the Burkert valve! The Cv value is not set in stone - my rough calculations tell me that Cv around 5-6 should be appropriate. The reason that I want to use a solenoid is that we need a fast reaction speed - we need to open the valve and close it again in about 300...
  12. johannestoger

    Proportional valve for water, low pressure

    Hi, We're designing a flow experiment where we need to produce a controlled pulse of water in a pipe. Our current design idea is based on a constant head tank, a flow meter, a proportional valve and a control system as follows: Image from Gharib et al. J Fluid Mech 1998. External factors...

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